Diffusers Path Traversal via weight_map Arbitrary File Read

Diffusers through 0.39.0, fixed in commit cee298c, contains a path traversal vulnerability in the _get_checkpoint_shard_files function that allows attackers to read arbitrary files by supplying malicious weight_map values in model index JSON. Attackers can use ../ sequences or absolute paths in weight_map entries to escape the model directory and read safetensors files outside the intended location during model loading.